Pre-engineered metal buildings have long been used for various types of structures, including, but not limited to, commercial building spaces such as warehouses, garages, auto-body shops, community centers, storage facilities, and more. Pre-engineered metal buildings typically require less labor and materials to produce, thereby reducing the costs with respect to typical residential or commercial buildings that utilize brick-and-mortar and/or wood framing. Often, entire sections of the pre-engineered metal building can be constructed off-site then shipped to the building site and installed or otherwise assembled with very few steps required.
One problem often associated with pre-engineered metal buildings is that metal sheeting on the outside walls and the roof of pre-engineered metal buildings allows water vapor to permeate therethrough and into the interior of the building or into the fiberglass layer on the inside of the metal sheeting. When water vapor is trapped in the fiberglass, or insulating layer, the thermal transfer through the insulation layer between the inside of the building and the outside of the building increases dramatically.
The principle function of a vapor barrier is to stop or retard the passage of moisture (water vapor) as it diffuses through materials. A vapor barrier or retarder is a material that offers more resistance to the diffusion of water vapor than most materials. The moisture diffusion control property of a material is called its “water vapor permeance” which provides a “perm rating,” as it is commonly referred to in the industry. A material typically needs to have a perm rating of less than 1.0 to be considered a vapor retarder. Most of the facing materials, such as the metal sheeting, used with fiberglass insulation in the pre-engineered metal building industry, have a perm rating of about 0.02.
Typical pre-engineered metal buildings currently utilize a layer of insulation having a vapor barrier, wherein the vapor barrier is inward-facing and the insulation is positioned against the inner surface of the outer metal sheeting of the building between the metal sheeting and the vapor barrier. This vapor barrier is often punctured, pierced, or the overall integrity is otherwise compromised during construction with the installation of doors, windows, HVAC systems, electrical systems, sprinkler systems, and the like are attached to the building framework.